1. Field of the Invention
The invention relates to a multiple-metal complex-containing compound and a metal complex, and manufacture method therefor as well as an exhaust gas purification catalyst manufacture method using the same. In particular, the invention relates to a method of manufacturing a metal particle having a controlled cluster size through the use of the multiple-metal complex-containing compound and the metal complex.
2. Description of the Related Art
A size-controlled metal cluster is different from a bulk metal in chemical characteristics, such as catalytic activity and the like, and physical characteristics, such as magnetism and the like.
In order to efficiently utilize the peculiar characteristics of the metal cluster, a method for easily synthesizing a size-controlled cluster in large amount is needed. A known method for obtaining such a cluster is a method in which (i) clusters of various sizes are produced by causing a metal target to evaporate in vacuum, and (ii) the thus-obtained clusters are separated according to cluster sizes through the use of the principle of the mass spectrum. However, this method is not able to easily synthesize a cluster in large amount.
The peculiar characteristics of the cluster is disclosed in, for example, “Adsorption and Reaction of Methanol Molecule on Nickel Cluster Ions, Nin+ (n═3-11)”, M. Ichihashi, T. Hanmura, R. T. Yadav and T. Kondow, J. Phys. Chem. A, 104, 11885 (2000) (non-patent document). This document discloses that the reactivity between methane molecules and platinum catalyst in the gas phase is greatly affected by the platinum cluster size, and that there exists a particular platinum cluster size that is optimal for the reaction, for example, as shown in FIG. 1.
Examples of utilization of the catalytic performance of a noble metal include purification of exhaust gas discharged from an internal combustin engine, such as an automotive engine or the like. At the time of the purification of exhaust gas, exhaust gas components, such as carbon monoxide (CO), hydrocarbon (HC), nitrogen oxide (NOx), etc., are converted into carbon dioxide, nitrogen and oxygen by catalyst components whose main component is a noble metal such as platinum (Pt), rhodium (Rh), palladium (Pd), iridium (Ir), etc. Generally, the catalyst component that is a noble metal is supported on a support made of an oxide, such as alumina or the like, in order to enlarge the contact area for exhaust gas and the catalyst component.
In order to support a noble metal on the oxide support, the oxide support is impregnated with a solution of a nitric acid salt of a noble metal or a noble metal complex having one noble metal atom so that the noble metal compound is dispersed on surfaces of the oxide support, and then the support impregnated with the solution is dried and fired. In this method, however, it is not easy to control the size and the number of atoms of the noble metal cluster.
With regard to such catalysts for exhaust gas purification, too, the supporting of a noble metal in the form of clusters has been proposed in order to further improve the exhaust gas purification capability. For example, Japanese Patent Application Publication No. JP-A-11-285644 discloses a technology in which a catalytic metal is supported in the form of ultrafine particle directly on a support through the use of a metal cluster complex that has a carbonyl group as a ligand.
Furthermore, Japanese Patent Application Publication No. JP-A-2003-481288 discloses a technology in which a noble metal catalyst having a controlled cluster size is manufactured by introducing a noble metal into pores of a hollow carbon material, such as carbon nanotube or the like, and fixing the carbon material with the noble metal introduced therein to an oxide support, and then firing it.
Still further, Japanese Patent Application Publication No. JP-A-9-253490 discloses a technology in which a metal cluster made up of an alloy of rhodium and platinum dissolved in the solid state is obtained by adding a reductant to a solution containing rhodium ions and platinum ions.
With regard to the metal complex, obtaining a polymer having an infinite number of metal atoms through the use of a polydentate ligand is known. For example, Japanese Patent Application Publication No. JP-A-2000-109485 discloses a technology for obtaining a dicarboxylic acid metal complex polymer having a giant three-dimensional structure through the use of a dicarboxylic acid.